In diabetic retinopathy and retinopathy of prematurity (ROP), damage to the retinal blood vessels creates regions of retinal hypoxia that express elevated levels of proangiogenic factors. Paradoxically, the angiogenic response induces not only revascularization of the damaged retina, but also pathological neovascularization (NV) into the vitreous, where it can cause blindness. The ideal therapy would suppress pathological NV without damaging intraretinal repair. Since VEGF is required for both intraretinal and intravitreal vessel growth, current therapies targeting VEGF cannot selectively inhibit NV. We recently found that the anti-inflammatory interleukin 10 (IL-10) is a powerful and selective inhibitor of pathological NV. In a mouse model of ROP, a single injection of IL-10 reduced NV 80% without impairing revascularization of the damaged retina. Although IL-10 has a short half-life (T1/2, 3 hrs in plasma), it reduced NV for 5 days. We hypothesize that IL-10 controls a pro-inflammatory process that initiates a cascade that directs angiogenesis away from the retina and into the vitreous. Selective inhibition of pathological NV has been demonstrated in mice genetically deficient in tumor necrosis factor alpha (TNF1) receptors, inducible nitric oxide synthase (iNOS) or cyclooxygenase-2 (COX-2). IL-10 suppresses expression of these in macrophages in vitro. The proposed research will test if the selectivity of IL-10 is dose-dependent and whether all NV could be arrested at higher concentrations, and whether it suppresses TNF1, iNOS, COX-2 or macrophage chemotactic peptide (MCP-1) expression in the retina. Aim 1 will also identify specific cell types (e.g. astrocytes, microglia, macrophages) involved in IL-10 regulated angiogenesis. Aim 2 will test whether reduced macrophage recruitment into the retina selectively inhibits pathological NV. Aim 3 will use quantitative RT- PCR to elucidate the effect of IL-10 on retinal expression of pro-inflammatory and pro-angiogenic factors, using known effects of IL-10 in macrophages as a guide. [unreadable] [unreadable] The long range goal of this research is to use the ROP paradigm to identify IL-10 sensitive events that drive pathological NV, and ultimately to find new therapies for diabetic retinopathy and ROP. [unreadable] [unreadable] [unreadable]